Residual pulp liquor oxidizing means



Nov. 20, 1956 L. F. KOOISTRA ETAL 2,771,460

RESIDUAL PULP LIQUOR OXIDIZING MEANS Filed Nov. 18, 1952 3 Sheets-Sheet l 6 M a a J r b o m C) /f E F I G. 9- U 20 INVENTORS 14/145157? 7' E AdO/STP/V -/?OBER 7' V. COBB BY a. I ATTO R N E Y Nov. 20, 1956 L. F. KOOISTRA ET AL 2,771,460

I RESIDUAL PULP LIQUOR oxwxzmc MEANS Filed NOV. 18, 1952 3 Sheets-Sheet 2 INVENTOR S lfl/ilBEAT/Z KOO/S 7/84 ROBE/7T V. C055 ATTO R N EY Nov.. 20, 1956 L. F. KOOISTRA ET AL 2,771,460

RESIDUAL PULP LIQUOR OXIDIZING MEANS Filed Nov. 18, 1952 3 Sheets-Sheet 3 INVENTORS A flMEEPT/J {00/5 7794 BY ROBERT v. C088 United States Patent 2,771,460 RESIDUAL PULP LIQUOR OXIDIZING MEANS Application November 18, 1952, Serial No. 321,114

4 Claims. c1. 23283) The present invention relates to apparatus for the stabilizationof sulphur compounds in residual liquors resulting from the digestion of cellulosicmaterials by the oxidation of the weak liquor at generally atmospheric temperatures and pressures.

The residual liquor resulting from the digestion of cellulosic materials in the sulphate process of paper pulp manufacturing contains sulphur compounds which are unstable when subjected to heat or heat in the presence of carbon dioxide gases. The principal unstable sulphur compounds in the pulp residual liquor sodium sulphide (NazS) and sodium organic sulphides, although smaller amounts of other unstable compounds, such as mercaptans, are also present. These sulphur compounds evolve noxious gases, such as hydrogen sulphide, during concentration and incineration of the residual liquor. Such noxious gases not only are a nuisance, but upon their escape from the process also involve an appreciable economic loss of sulphur. However, it is known in the art that the unstable sulphur compounds can be stabilized by oxidation of the liquor in contact with an oxygen containing gas, such as air, at generally atmospheric temperatures and pressures. The oxidation of the liquor converts the sodium sulphide, for example, to a stable compound, sodium thiosulphate (NazSzOs).

The present invention relates to apparatus for the oxidation of residual liquor under conditions of a minimum formation of foam. The liquor is passed through a tower in a plurality of films in intimate surface contactwith the oxidizing gas, with the liquor films'formed at the top of the tower in such a manner as to avoid the passage of oxidizing gases through any body or solid stream of liquor. Any foam formed in the lower portion of the tower is removed, as formed, so as to avoid pluggage of the gas flow passages through the upper portion of the tower.

The various features of novelty which characterize this invention are pointed out with particularity in the claims annexed to and forming a partof this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which the invention has been illustrated and described.

'Of the drawings:

Fig. 1 is an elevation view, partlyin section, of an oxidation tower constructed in accordance with the present invention;

Fig. 2 is an enlarged elevation view, in section, showing the liquor supporting panels with their positioning means;

Fig. 3 is a section view taken on the line 33 of Fig. 2;

Fig. 4 is an enlarged section of a portion of the apparatus shown in Figs. 1 and 2;

Fig.5 is an enlarged section taken on the line 5-5 of Fig. 4;

Fig. 6 is an enlarged section of a portion of the apparatus shown in Figs. 1 and 2;

v Fig. 7 is a side view of a liquor spray nozzle;

Fig. 8 is an end view of the nozzle shown in Fig. 7; and

Fig. 9 is a perspective view of an alternate liquor distribution structure.

In general, as shown in the drawings, the liquor oxidizing apparatus of the present invention includes a vertically elongated shell 10 of rectangular cross-section defining a tower 11 having an air inlet and a liquor outlet at the bottom, and an air outlet and liquor inlet at the top thereof. Means are provided within the tower for surface contact between films of liquor and a gaseous oxidizing medium, such as air. The contact is accomplished with a minimum of foam formation in the area of liquor-air contact, with any foam formed withdrawn from the lower portion of the tower by means of a positive displacement foam pump, or the like, for delivery to a settling tank (not shown).

Referring particularly to Fig. l of the drawings, the tower 11 is provided with an air inlet opening 12 at one side of the lower end thereof. Oxidizing air is delivered by a blower 13 through a duct 14 into a housing 15 enclosing lower end portion of the tower. The duct 14 is provided with a steam coil air heater 16 so that the oxidizing air can be preheated, if desired, before delivery to the tower 11. Ordinarily, it is desirable to preheat the oxidizing air so as to avoid cooling the liquor. Any reduction in the temperature of the oxidized liquor requires additional steam in the multiple-efiect evaporators which is not only uneconomical, but also tends to reduce the evaporator capacity. Very little, if any, concentration of the liquor is accomplished in the oxidizing tower.

The housing 15 enclosing the lower end of the tower not only provides an enclosure to direct flow of air into the tower, but also provides the exterior walls for a reservoir 17 for the accumulation of oxidized liquor within the lower portion of the tower. Ordinarily, the upper level of oxidized liquor is maintained within the reservoir at a position 18, approximately as shown. Immediately above the normal liquor level, an opening 20 is provided in the housing 15 on the side thereof opposite the air inlet 12, for the removal of foam which may be formed within the tower. This foam may be withdrawn by a positive displacement pump (not shown) or may be permitted to overflow through the opening 20. Any foam removed from the unit is delivered to a settling tank (not shown) where the foam is dissipated, and the liquor recovered from the foam returned to the process.

The oxidizing air introduced to the tower through the opening 12 passes upwardly between closely spaced wall surfaces which support films of liquor for extensive liquorair contact, as hereinafter described. After passing through the air-liquor contact portion of the tower, the air is discharged through horizontally disposed ducts 21 and 22 positioned on opposite sides of the tower and connected with an external stack or discharge pipe (not shown) leading to the atmosphere. As shown, the discharge ducts 21 and 22 are horizontally elongated and are in communication with the spaces between the parallel walls supporting the films of liquor, so that the air in discharging from the tower does not pass through any body of stationary or stream of moving liquor.

Pulp residual liquor obtained from washing the digested wood chips in the manufacture of pulp and paper is delivered to the oxidizing tower 11 through pipes 23 which are connected with a plurality of horizontally extending manifold headers 24 by individual vertical pipes 25. The residual liquor is of low concentration, usually with a solids content of 13 to 18 percent, and readily flows through the conduit system. Each header is provided with a plurality of depending stub-pipes 26 which in turn discharge liquor sprays downwardly through nozzles 27. With the pipe and manifold arrangement described each 3 of the nozzles is spaced above the upper end of the liquor film supporting walls of the apparatus.

As shown, the nozzles 26 discharge a relatively coarse spray of liquor downwardly in a pyramidal pattern so that liquor is distributed to the upper ends of the liquor film supporting walls of the tower, and overlapping of the spray from adjacent nozzles is minimized.

According to the invention a plurality of depending panels are suspended within the tower in closely spaced parallel planes. The panels extend across the tower and for a major portion of the tower height, to present an extensive surface for contact between liquor and oxidizing air. The individual panels may be of one piece or segmental construction providing the segmental construction forms a continuous uninterrupted planar surface from top to bottom of the panel. The panels are perforated so that the deposition of liquor on one side of the upper end of the panel permits liquor film formation on both sides of the panel. In the preferred construction shown in the drawings, the panels are formed of woven wire screens 28 having a width sufficient to extend from side to side of the tower. To obtain large areas of surface for contact between the films of liquor on the panels and the oxidizing air, the panels are closely spaced in parallel substantially vertical planes.

In the illustrated embodiment of the invention, each of the screens 28 is supported at its upper end from the structural steel work of the tower and is provided with counterweighted means at its lower end to maintain the positional relationship of the adjacent screens.

The upper support means for each of the screens 28 is particularly shown in Figs. 2, 4, and 5, and includes a plate member 30 embracing the upper end portion of the screen, with the plate member hung from a beam 33 by a bolt 31 which is attached to the member 30 by a clevis 32. The beam 33 extends along the edge of the tower 11 in a direction normal to the planes of the screens 28 and is formed by a pair of channel members arranged back to back with a horizontal space therebetween to accommodate the bolts 31. The upper end of each bolt 31 is provided with a nut 34 which rests directly upon a plate 35 on the top of the beam 33. As shown in Figs. 2, 3, and 4, a pair of channel member 36 support the pipe 23 from the beams 33 on each side of the tower. The beams 33 are framed into the structural steel work supporting the tower.

Each clevis 32 is provided with a recess 37 to receive the upper edge of the plate member 30 which embraces both sides of the upper end portion of the screens 28 for the full horizontal length thereof. The plate member is attached to the clevis by suitable means such as a machine screw 38 (see Figs. 4 and The plate member 30 is formed from light gauge metal, extends the full length of a screen 28 and is bent around the end of the screen to encase the end portion thereof. The screen end portion and the plate member is bent to form a V-shaped vertical cross section, with the legs of the V-ending in the vertical plane of the screen. The apex 40 of the V-section has a height equal to the spacing between parallel adjacent screens. With this construction the displaced portion of the plates 30 provides an inclined surface to receive any droplets of liquor discharged in a vertical direction from the spray nozzles 27.

An alternate means for distributing residual liquor to the upper ends of woven wire screens is shown in Fig. 9. where a distributing trough 55 is installed at one side, or both, of the upper end portion of a plurality of film supporting screens 28'. The trough is supplied with residual liquor through an inlet pipe 56, which is normally submerged beneath the pool of liquor maintained in the trough. A series of V-notch weirs are provided in the side and intermediate the height of the trough for a distributed discharge of liquor over a plurality of liquor fiow guiding plates 57. Each of the plates extends from one side of one of the V-notch weirs to the upper end of one of the screens 28. With this construction one weir supplies liquor to two adjacent screens, and with the weirs maintained at a common level, the distribution to each of the screens will be substantially equal to flow to all screens. In such an arrangement the upper end portions of the screens need not be displaced as in the arrangement shown in Figs. 1, 2, and 3.

The means maintaining tension on, and the horizontal spacing of, the screens 28 and 28' is indicated in Figs. 1, 2, and 6, and consists of a plate 41 bent around the lower end of and embracing the end portion of each screen. The plate 41 and screen are attached at spaced positions to I-beams 42 which extend in a horizontal direction normal to the plane of and below the lower edget of the screens 28.

In the illustrated embodiment of the invention a beam 42 is positioned near each end of the screens with a third beam 42 near the transverse center of the screen. The attachment between each of the I-beams 42 and the lower edge of the screens is accomplished by a pair of clevis 43, which are similar in construction to the clevis 32, with the recessed end thereof embracing the plate 41 and screen end portion and secured thereto by machine screws 44. Each clevis 43 is attached to the flange of an I-beam 42 by a threaded bolt 45. The beams 42 are welded to an I-beam 46 which is horizontally positioned generally parallel to the screens 28. The beam 46 is pivotably attached by a pair of links. 47 to a pair of lever arms 48. Each link is pinned to the beam 46 on one side of the beam midpoint, while the companion link 47 is pinned on the opposite side of thebeam midpoint. In the embodiment shown, the pinned connection between a link 47 and lever arm 48 is located approximately of the length of the arm from a pinned fulcrum 50. The pinned fulcrum connection of the lever arm 48 is to a fixed position structural beam 51 in the oxidized liquor reservoir 17. The free end of each lever arm 48 is loaded by a counterweight 52 which is attached by means of a rod 53 pinned to the end of the arm 48.

In the screen 28 support and positioning structure described, the upper end of each screen is located in a level position by adjustment of the nut 34 on the threaded bolts 31, with the upper edge of all of the plates being substantially in a common horizontal plane. The proper amount of tension on the lower end of each screen is attained by adjustment of the threaded bolts and the weight 52 so that the spacing between adjacent screens will be substantially uniform at the top and bottom. Spacers are used intermediate the height of the screens to maintain the horizontal spacing between the screens. The spacers may take many forms, as for example, spring clips supported on the screen and abutting an adjacent screen.

Customarily, the residual liquor is delivered from the pulp washers to the oxidizing tower with a solids content of approximately 13 to 18 per cent, although the solid concentration may vary both above and below this value in some pulp producing plants. Since one of the greatest advantages of a screen or perforated panel is the formation of a thin downwardly moving film of liquor across the openings thereof, whereby both sides of the film is contacted by the oxidizing air, the openings should be dimensioned to permit such film formation. It is also desirable to select a screen or perforated panel having large openings so as to reduce the weight and cost of the film supporting surfaces. With liquor having a solids content of 13 to 18 percent, a screen having generally square openings of the order of 7 to inch on a side will support a liquor film covering the opening. With a higher solids content in the residual liquor, the openings in the screen can be enlarged, while with a lower solids content the openings must be reduced for satisfactory operation.

By way of example and not of limitation, an oxidizing tower of the type described was constructed with woven wire screens of 4 x 4 mesh having .063 inch diameter wire. Each screen was six feet wide and forty-four feet long. The tower contained 182 screens installed on one inch centers. With approximately 96,000 square feet of liquor film exposed to oxidation by air, 2000 pounds of sulphides, expressed as NazS, was oxidized per day (24 hours) in contact with from 4 to cubic feet of air per gallon of liquid. Liquor flow rates varied between 450 and 650 gallons per minute.

While in accordance with the provisions of the statutes we have illustrated and described herein the best form and mode of operation of the invention now known to us, those skilled in the art will understand that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention covered by our claims, and that certain features of our invention may sometimes be used to advantage without a corresponding use of other features.

What is claimed is:

1. In a tower for oxidizing residual liquor including means for passing air through said tower as an oxidizing medium, a reservoir in the lower portion of said tower, a plurality of upright closely horizontally spaced screens extending transversely across said tower and projecting downwardly beneath the surface of the oxidized liquor normally maintained within said reservoir, imperforated plate means embracing the upper end portion of each of said screens, each of said plate means bent in a V-shaped vertical section with the apex thereof in general vertical alignment with the upright plane of an adjacent screen and with adjacent plate means positioned in horizontally spaced nested relationship, and a plurality of spray nozzles disposed above the upper ends of said screens to deposit residual liquor on the upper end portions of said imperforated plates.

2. In a tower for oxidizing pulp residual liquor including a liquor reservoir in the lower portion of said tower, a plurality of upright screens arranged in closely spaced parallel planes extending across said tower and from the upper portion of the tower to a position submergedbeneath the liquor normally maintained in said reservoir, a plate member embracing the upper end portion of each of said screens, said plate members being of V-shape in vertical section with the ends of the legs of the V-shape lying in the plane of the associated screen and the apex of the plate lying substantially in the plane of an adjacent screen, means for maintaining the horizontal spacing of said screens, means for passing air upwardly through the intermediate portion of said tower between said screens, and a plurality of horizontally spaced liquor spray nozzles disposed above said screens and arranged to deposit liquor droplets upon said plate members whereby films of residual liquor flow downwardly along the screens in oxidizing contact with said air and discharge into said reservon.

3. In a tower for oxidizing pulp residual liquor includ ing a liquor reservoir in the lower portion of said tower, positive displacement pump means for withdrawing foam from said reservoir at a position above the normal liquor level maintained within said reservoir, a plurality of upright screens arranged in closely spaced parallel planes extending from side to side of said tower and from the upper portion of said power to a position submerged in said liquor reservoir, a plate member embracing the upper end portion of each of said screens, each of said plate members displaced to incline across the space between adjacent screens, means associated with the lower ends of said screens for maintaining tension on said screens, means defining an inlet opening in said tower for oxidizing air positioned upwardly adjacent said liquor reservoir, means defining an air inlet opening in said tower positioned downwardly adjacent said plate members, and a plurality of liquor spray nozzles arranged to project a pyramidal spray pattern of liquor droplets upon said plate members whereby films of residual liquor flow downwardly along both sides of said screens in oxidizing contact with said air and discharge into said reservoir.

4. In a tower for oxidizing pulp residual liquor including means for passing air through the intermediate height of said tower as a liquor oxidizing medium, a liquor reservoir in the lower portion of said tower, means for withdrawing foam from said reservoir at a position above the normal liquor level maintained within said reservoir, a plurality of upright screens arranged in closely spaced planes parallel to the flow path of said air and extending throughout the horizontal cross section area of said tower, a plate member embracing the upper end portion of each of said screen and inclined toward an adjacent screen, each of said plate members displaced out of the plane of each of said screens, tension means engaging the lower ends of said screens for maintaining the horizontal spacing of said screens, and a plurality of horizontally spaced liquor spray nozzles disposed above said screens and arranged to deposit liquor droplets upon said plate members whereby films of residual liquor flow downwardly along the screens in oxidizing contact with said air and discharge into said reservoir.

References Cited in the file of this patent UNITED STATES PATENTS 782,190 Clough Feb. 7, 1905 1,098,487 Doherty June 2, 1914 2,570,460 Kress Oct. 9, 1951 FOREIGN PATENTS 675,831 France Feb. 14, 1930 427,087 Great Britain Apr. 16, 1935 65,078 Switzerland July 22, 1913 

1. IN A TOWER FOR OXIDIZING RESIDUAL LIQUOR INCLUDING MEANS FOR PASSING AIR THROUGH SAID TOWER AS AN OXIDIZING MEDIUM, A RESERVOIR IN THE LOWER PORTION OF SAID TOWER, A PLURALITY OF UPRIGHT CLOSELY HORIZONTALLY SPACED SCREENS EXTENDING TRANSVERSELY ACROSS SAID TOWER AND PROJECTING DOWNWARDLY BENEATH THE SURFACE OF THE OXIDIZED LIQUOR NORMALLY MAINTAINED WITHIN SAID RESERVIOR, IMPERFORATED PLATE MEANS EMBRACING THE UPPER END PORTION OF EACH OF SAID SCREENS, EACH OF SAID PLATE MEANS BENT IN A V-SHAPED VERTICAL SECTION WITH THE APEX THEREOF IN GENERAL VERTICAL ALIGNMENT WITH THE UPRIGHT PLANE OF AN ADJACENT SCREEN AND WITH ADJACENT PLATE MEANS POSITIONED IN HORIZONTALLY SPACED NESTED RELATIONSHIP, AND A PLURALITY OF SPRAY NOZZLES DISPOSED ABOVE THE UPPER ENDS OF SAID SCREENS TO DEPOSIT RESIDUAL LIQUOR ON THE UPPER END PORTIONS OF SAID IMPERFORATED PLATES. 